Let's say it's Saturday night, and you have the option of going to a party or seeing a movie. If you choose the movie, and an hour into it you realize it's the worst movie ever made, do you stick around for the remaining hour? Many people would say "well, I already paid for the movie, I might as well stay". A more rational person would say "well, I'm already out the $10 I paid for a ticket (a sunk cost), I might as well leave and go to that party instead."
Same thing with this kid. It doesn't matter how long he's been with the team or how many hours of practice he's gone through; those are sunk costs that aren't recoverable, and should have no bearing on whether he wants to stay with the team for the remainder of the season.